1. Field of the Invention
The present invention relates to a mobile communication terminal, and more particularly, to a cell selecting apparatus for a mobile communication terminal capable of performing a cell selection by using a message transmitted through a channel, and a method thereof
2. Description of the Background Art
Generally, a wireless communication system provides various communication services comprising audio data and video data to a user by using a modulating technique such as code division multiple access (CDMA), time division multiple access (TDMA), or the like. The CDMA system provides at least one CDMA technique such as a TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, the 3GPP (3rd Generation Partnership Project) standard or the like. A service area defined by one base station of the CDMA system is referred to as a cell. Since the cell can provide service to mobile communication terminals inside the cell area, a provider can provide service to a user anytime anywhere by overlapping a plurality of cells.
When the mobile communication terminal (hereinafter, referred to as ‘mobile terminal’) moves to another cell area, the mobile terminal and the system have to continuously provide service to the user. Accordingly, when the mobile terminal is in an idle state, a cell selection is performed, and when the mobile terminal is in a connected state, a handover is performed.
When the mobile terminal in an idle state moves between cells, the mobile terminal releases a connection to a current cell for service (a serving cell). Then, the mobile terminal performs a connection to a neighboring cell.
FIG. 1 is a flowchart showing a cell selecting method in a mobile communication terminal in accordance with the related art.
Referring to FIG. 1, the related cell selecting method is performed by the following formulas.Squal=Qqualmeas−Qqualmin   formula (1)Squal<=Sreference   formula (2)
In the formulas (1) and (2), the Qqualmeas denotes a reception power quality of a serving cell measured by the mobile terminal. As one example, the Qqualmeas includes an Ec/lo for denoting a ratio between a reception power of the serving cell and an interference signal. The Qqualmin denotes a minimum reception power quality of the serving cell for enabling the mobile terminal to continuously perform service. The Sreference denotes a reference value used for connecting the mobile terminal to the neighboring cell, and is stored in the mobile terminal.
The mobile terminal that has calculated the reception power quality of the serving cell by the formulas (1) and (2), calculates a ranking of the serving cell, RANKs and a ranking of the neighboring cell, RANKn.RANKs=Qmeas,s+Qhyst,s   formula (3)RANKn.=Qmeas,n+Qoffsets,n   formula (4)
In the formulas (3) and (4), the Qmeas,s denotes a reception power quality of a serving cell measured by the mobile terminal, and the Qmeas,n denotes a reception power quality of a neighboring cell measured by the mobile terminal. The Qmeas can denote an Ec/lo measured by the mobile terminal or a received signal code power (RSCP) for indicating a power of a common pilot channel. The Qhyst,s denotes an offset value of a serving cell, and the Qoffsets,n denotes an offset value of a serving cell versus a neighboring cell.
In the related art cell selecting method, Squal is calculated and then is compared with Sreference. If the Squal is less than the Sreference, a ranking of a neighboring cell, RANKn and a ranking of a serving cell, RANKs are calculated and then are compared with each other. If the RANKn is greater than the RANKs for a certain time, the mobile terminal performs a cell selection from the serving cell to the neighboring cell.
However, the related art cell selecting method has the following disadvantages. First, in case that the neighboring cell has an excellent reception power quality, the mobile terminal performs unnecessary cell selection even if the mobile terminal is in a serviceable state. As the number of times that the mobile terminal performs unnecessary cell selection is increased, the battery consumption amount of the mobile terminal is increased undesirably.
In order to solve such problem, a method for comparing a pilot power of the serving cell with a preset reference value in a cell selecting process is disclosed in the U.S. patent application publication 2004/0043769. However, the method performs a cell selection only based on a received pilot power of the serving cell without considering substantial channel environments, thereby not allowing a precise cell selection to be performed.